1. Field of the Invention
The current invention is directed to the mixture of two reactive resin streams within the entrance of a pultrusion die. The resin streams are mixed adjacent fibers being pultruded through the die, the resin streams wetting the fibers. An ultrasonic driver agitates the resins and fibers to accelerate the rate of fiber wettability.
2. Description of the Prior Art
As noted in U.S. Pat. No. 4,793,954, an ultrasonic driver may be used to improve thermoplastic extrusion or injection rates. The ultrasonic vibration from the driver desirably is applied to the extrusion or injection die in a direction parallel to the flow of the thermoplastic material.
In U.S. Pat. No. 4,500,280 a vibrating feed device is placed between an injection head and a mold. The device vibrates the thermoplastic molding material that flows from the injection head into the mold. This vibration improves the flow and distribution of the molding material and the quality of the molded article.
U.S. Pat. No. 3,169,589 also discloses that solid or semi-solid plastic or flowable consolidated materials can be made to extrude, i.e., pass through an orifice or tube, when soundwaves are applied to the materials, or to the extrusion die, or both.
Reference also U.S. Pat. No. 2,408,627 wherein relatively rapid vibrations are imparted to an extrusion apparatus and preferably to the extrusion die by a device such as an electric or electromagnetic vibrator. The rate and amplitude of the vibrations may be adjusted. The invention of the '627 patent relates to the extrusion of non-metallic plastic material.
Ultrasonic vibrations may also be used to improve the processability of materials other than the thermoplastic materials noted in the above patents. Reference, for example, the vibration apparatus of U.S. Pat. No. 3,456,295 used to coat welding rods with welding flux, wherein the apparatus is operated in the range from about 5,000 to about 400,000 cycles per second.
In U.S. Pat. No. 3,737,261 sonic drivers are used to help saturate fibers with an already-mixed thermoset resin.
Let us now consider the reaction injection molding (RIM) process.
As noted in the article "RIM-pultrusion of Thermoplastic Matrix Composites", authored by Mr. H. Ishida and Mr. G. Rotter, presented Feb. 1 through May 1988 at the 43rd Annual Conference of the Composites Institute, RIM denotes a process in which two low viscosity polymer precursors are brought together in an impingment mixer (FIG. 1) where they begin to react, before traveling on to fill a mold. The low viscosity of the resins reduces the pumping requirements and leads to better resin penetration of the mold and reinforcement. RIM is limited, however, in that it is generally a batch operation and is at a cost disadvantage with continuous processes. Furthermore, it is difficult to produce RIM parts with continuous fiber reinforcement.
The continuous fiber-reinforcement pultrusion process (FIG. 2) combines catalyzed resin and fiber reinforcement in a resin tank prior to the resin-soaked fiber being pulled through a heated die by pullers and thereafter cut to a particular length. Generally, the resin tank contains mixed thermosetting resins which undergo some degree of cure in the tank over time. The viscosity of the resins in the tank thereafter increases over time. If the mixed resins thicken sufficiently the machine will stall.
These factors have generally limited the pultrusion process to blended resin materials with relatively long pot lives.
In the above publication, Mr. Ishida and Mr. Rotter suggest that the resin tank be replaced by the resin impregnation chamber as shown in FIG. 3. It is in this chamber that the wet-out of the reinforcement occurs. The authors suggest that the limitations of each individual technique have been avoided such that the pot life restrictions of the resin tank are drastically reduced by the use of materials with short gel times and low viscosities. The authors suggest that many resin chemistries previously unavailable for pultrusion can now be used. The process is equally applicable to thermoset RIM systems as demonstrated by the production of urethane pultrusions.
One resin system for this suggested pultrusion process is disclosed in U.S. Pat. No. 4,735,992, wherein a pre-mixed blend of reactive resin streams feeds a die having a glass fiber core continuously pulled therethrough, as noted in column 3, line 57 through column 4, line 8 of this '992 patent. Note that, once again, the resin is pre-mixed prior to saturation of the glass fiber core.
Mr. Ishida et al. suggest in FIG. 4 a possible resin chamber design wherein already mixed resin components are introduced from above to wet fibers entering the chamber at an angle. A nitrogen blanket may be provided if needed, for sensitive RIM chemistries.
For initial studies, Ishida adopted the more basic design shown in FIG. 5A. This chamber still has the hydrostatic squeezing advantage of the FIG. 4 design, but now has dead zones along its length. It can be expected that in these dead zone areas the resin will stagnate and cure prematurely, possibly even leading to the formation of a resin plug (FIG. 5B) which would stall the machine. The resin could also cure to possibly form a sheet or funnel about the inner diameter of the wall, so subsequent material would flow more easily, as shown in FIG. 6.
All of these problems of course originate from the pre-mixing of the two co-reactive resin streams earlier than absolutely necessary. A process needs to be developed wherein the co-reactive resin streams are mixed together at the last possible moment. The process must include some compensatory device to increase fiber wet out, at the point of saturation, since there no longer exists in the process a large resin tank for wetting the fibers, nor a resin chamber fed with pre-mixed resin.